HONG KONG -- Volkswagen Group could reach a final settlement with U.S. authorities as early as October over its large-engine diesel cars found to have cheated emissions tests, the sales chief of its premium Audi brand said.

Negotiations related to the 3.0-liter engine in VW, Audi and Porsche vehicles were progressing well, Dietmar Voggenreiter, Audi's global head of sales and marketing, told Reuters today in an interview in Hong Kong.

Voggenreiter said VW Group is in "really good discussions" with U.S. authorities. "Hopefully in October, latest the beginning of November, we will have the final agreement with the U.S.," he said.

VW last September admitted using manipulated engine management software to cheat on exhaust emissions tests. The automaker agreed with U.S authorities in June to pay up to $15.3 billion for car buybacks and fixes to 475,000 2.0-liter VW and Audi diesel vehicles fitted with the emissions-cheating software.

That accord did not include fixes for 85,000 VW, Audi and Porsche 3.0-liter engine cars that could potentially cost billions more if the automaker needs to buy them back.

Voggenreiter said the U.S. negotiations, which related to four-cylinder VW diesel engine cars and 3.0-liter V-6 engine Audi vehicles, were still ongoing and unresolved. "We are just in discussions so I cannot judge how the authorities will judge our technical solutions; but I feel we have good technical solutions," he said.

The scandal has hurt VW's reputation and business, and already cost the German carmaker billions of dollars - not including any U.S. settlement on the large-engine diesel vehicles.